In various fields or industries, three-dimensionally molded components are produced by arranging a mass of fibrous material, and then heating, press-molding and cooling the fibrous mass to produce the molded fiber component. In the automobile industry such three-dimensionally molded components of fiber material are used as interior finish and trim components, as a backing for such finish and trim components, and especially also as sound insulation or noise damping components for motor vehicles. For example, such molded fiber components are used as fire wall insulation to damp engine noise, and as a floor sound insulation or floor pan liner to damp road noise, drive train noise and other driving noises. These components also offer thermal insulation for the passenger compartment of the motor vehicle. Such acoustic damping or insulating components are also used in the motor vehicle trunk, head liner, door paneling or trim, package shelf and engine compartment. It has been found to be especially suitable to produce such sound insulation components as molded fiber components by three-dimensionally molding a fiber fleece material. These molded fiber components especially consist of thermally deformable (e.g. thermoplastic) synthetic fibers, or of a mixture of natural fibers and/or thermoset fibers together with thermoplastic fibers.
These molded fiber components are to be fabricated as rather large surfacial parts, which are correspondingly to be applied over large surface areas of the motor vehicle, such as the floor pan and the head liner. However, over their relatively large surface area, these components often must include distinct sub-areas that have different thicknesses and/or different densities of the fiber material, in order to achieve different sound-damping and sound-insulating characteristics at the corresponding different locations of the motor vehicle. It is further necessary that such molded components should be as light-weight as possible so as to avoid unnecessarily increasing the weight of the motor vehicle, or requiring an excessive amount of fibrous raw material and therefore unnecessarily increasing the manufacturing costs. Thus, it has become important to be able to fabricate such a molded fiber component with a precisely targeted variation of the thickness and the density of the fiber material in different sub-areas, to precisely meet the requirements respectively pertaining for the different sub-areas. It is also often necessary that such molded fiber components must include openings or cut-out areas for accommodating or fitting other parts of the motor vehicle.
It has long been known in the automotive industry that such molded fiber components with varying thicknesses and varying densities in different sub-areas can be produced by providing a uniform fiber base or substrate, and laying-up extra layers or blocks of fiber material onto the fiber base in particular areas that require a greater thickness and/or greater density of the fiber material. During the molding process, the additional fiber layers or blocks are adhesively bonded and laminated onto the fiber base, and the whole assembly is three-dimensionally molded at an elevated temperature, and then cooled to set or fix the molded configuration. Any required openings are cut-out thereafter by stamp-cutting, water jet cutting, or the like. Such a process is disadvantageous in view of the significant additional labor steps and associated extra cost.
To avoid the need for laying-up individual layers and/or blocks of fiber material, improved methods and apparatus have been developed, whereby a fiber fill material of loose fibers or strands is blown or sprayed onto or into a mold, which then three-dimensionally molds the accumulated fiber mass at elevated temperature, followed by cooling, in order to produce a fixed three-dimensionally molded fiber component. In this regard, see U.S. Pat. Nos. 5,942,175, 4,806,298 (as well as the related German Patent laying-open document DE 35 41 073), and U.S. Pat. No. 7,622,062 (as well as the related WO 2004/106042 and DE 103 24 735 and US 2007/0007695). Generally, these documents disclose similar basic aspects of a method and apparatus for producing a three-dimensionally molded fiber body. A mold including a lower mold tool and one or more upper mold tools with various different three-dimensionally contoured mold surfaces of perforated sheet metal is filled with a fiber mixture by blowing or streaming the fiber mixture into the mold. For example, this is achieved via a movably controlled fiber fill pipe into an open mold, or via a fiber injection nozzle into a closed mold. Then a hot airstream at about 200° C. is blown through the accumulated fiber material between the upper and lower mold tools, such that the synthetic plastic fibers of the fiber mixture partially melt and/or such that thermosetting binder materials are activated, whereby the meltable thermoplastic materials or the thermosetting materials form a binder for the other fibers of the fiber mixture. The fiber mixture is then three-dimensionally molded under pressure between the mold tools. Thereafter cooling air is blown through the molded fiber body in the mold so as to cool, stabilize and fix the molded shape of the resulting fiber pre-form. The fiber pre-form and/or the mold tools can be moved among various stations, e.g. a filling station, a heating station, and a cooling station, by a rotary table arrangement or by a linear slide table arrangement.
The abovementioned conventional methods and systems for producing three-dimensionally molded fiber components all suffer several disadvantages. It is especially a problem that these known methods have not been able to satisfactorily achieve the desired variation of the thickness and/or density of the fiber material at different sub-areas of the molded component, with sufficient accuracy and sufficient economy. Namely, the placement and positioning of the desired fiber quantity and fiber density in the different sub-areas, in relation to the prescribed molding contour, is rather complicated and difficult, and also rather inaccurate as to the location, especially at the areas of transitions of thickness or density, for example at transitions of the molding contour with a thickness jump from a small wall thickness (e.g. 8 mm) to a significantly larger wall thickness (e.g. 40 to 60 mm). Due to a rather inaccurate blowing-in or streaming-in of the fibers with an airstream while simultaneously applying vacuum suction in the three-dimensionally contoured mold tool, this leads to an excessive accumulation and layering or superposition of the applied fiber quantity in such areas of a contour transition. As a result, only rather inaccurate surface densities and thicknesses of the molded component can be achieved especially in the areas of contour transitions. It has not been possible to achieve an exactly determined position of such transitions of the thickness and/or the density of the applied fiber quantity, with precise boundaries between adjacent sub-areas having different thicknesses and/or densities. Furthermore, the need of a subsequent cutting step to produce the required holes or openings in the molded fiber component entails additional costs, due to the additional handling, additional equipment, additional tooling, and additional work steps. This disadvantageously increases the cost of producing the finished molded component. A further disadvantage is that the fiber material is introduced, heated, consolidated or compressed and molded, and finally cooled in the same mold tool, which thus requires this mold tool to be repeatedly heated and cooled. That in turn leads to a relatively high energy consumption and also relatively long mold tool and process step cycle times. Still further, the application of a vacuum through a perforated sheet metal mold tool, over the entire area of the component to be molded, leads to a relatively high consumption of the vacuum suction airflow, which again leads to relatively high energy consumption.
To achieve some improvement over such disadvantages of the above prior art, another fiber molding method and apparatus has also become known in the industry. In this method and apparatus, a perforated sheet metal molding shell is positioned on top of a conveyor belt. Vacuum is applied via a vacuum box to the upper side of the perforated molding shell selectively through plural trap-door vacuum valves that individually communicate with different segments of the perforated molding shell. The loose fiber fill material is blown horizontally into the space between the conveyor belt and the upper mold shell, while vacuum is applied successively sequentially through the individual trap-door vacuum control valves to successive sequential areas or segments of the mold shell beginning at the far end away from the fiber blow-in entrance. Thereby, the amount of vacuum airflow can be somewhat reduced, and the successive filling of the mold chamber with the fiber material successively from one end to the other is facilitated and made more uniform. While this produces a fiber mass with different thicknesses in different sub-areas, corresponding to the configuration of the upper mold shell, it is not possible to accurately produce significantly different fiber densities at different areas with distinct or crisp transitions of the fiber density precisely at predefined locations. After the molding shell is filled with fibers in this manner, the molding shell is lifted away, and the resulting fiber mass is transported by the conveyor belt into a hot air oven, where the fibers are heated and partially melted. After the heating process, the fiber mass is transported into a separate cooled mold station including upper and lower mold tools, between which the hot fiber mass is three-dimensionally molded into the desired final contoured shape and cooled so as to fix and stabilize this contoured shape. Thus, this process and apparatus involve a division of the processes into three distinct process cycle steps and three distinct stations, namely the first step and station for forming the fiber mass, the second step and station for heating the fiber mass, and the third step and station for the final molding and cooling of the fiber mass to form the fiber pre-form. This separation of the heating and cooling achieves economic advantages, because the total energy required for the heating and cooling can thereby be reduced. Nonetheless, the disadvantage remains, that it is not possible to achieve the desired variation of the thickness and density of the fiber mass with good precision especially at the predefined locations of the transitions of the thickness and/or density between adjoining sub-areas of the fiber pre-form that is to be produced.